The newest generation of global coupled atmosphere-ocean-ice models at the National Center for Atmospheric Research contains a significant development in the sea ice model components. The Community Climate System Model version 2 (CCSM-2) and the Parallel Climate Model/CCSM Transition Model (PCTM) both include a multi-category ice thickness distribution model, multiple temperature layers, and the elastic-viscous-plastic ice dynamics. The ice model improvements, along with developments in the atmospheric and ocean models, produce a better simulation of both the Arctic and Antarctic sea ice covers, with more realistic physical processes. The PCTM is being used for ensembles of climate simulations of 1870 to present and to 2100 with increasing greenhouse gases, sulfate aerosol loading, volcanic signals and solar variability. The trends of the polar climate and sea ice in the PCTM in these simulations will be compared to the observed record. Recent evidence of thinning sea ice in the Arctic will be compared to the modeled natural variability and the simulated trend.